Osteosarcoma: Radiographic Features and Imaging Strategies
Prepared for RadiologyWeb by Joseph A Gagliardi, M.D.
Table of Contents
Introduction
Part 1: Intramedullary Osteosarcoma
Part 2: Surface Osteosarcoma
Part 3: Secondary Osteosarcoma
Part 4: Extraskeletal and Gnathic Osteosarcoma
References
Figure Legend
Part 2: Surface Osteosarcoma
Contributing Authors: Lustberg H1, Gagliardi JA1, Lawson JP2, Lawson AJ3, Fugate M1, Micalizzi GJ1, Specht NT1.
- Department of Radiology, St. Vincent's Medical Center, Bridgeport, CT.
- Department of Radiology, Yale University, New Haven, CT.
- Department of Radiology, Waterbury Hospital, Waterbury, CT.
Surface osteosarcoma accounts for approximately 4-10% of all osteosarcomas. These lesions include, in decreasing order of frequency, parosteal, periosteal, high grade surface, intracortical, and a recently described osteochondroma-like parosteal osteosarcoma.
Parosteal osteosarcoma begins in the outermost layer of the periosteum and, like conventional intramedullary osteosarcoma, these tumors are most commonly found around the knee, particularly the distal femur, where they are metaphyseal in location [1].
Histologically, these lesions have variable fibrous, osteoid and cartilaginous elements, which can be mistaken for fibrous dysplasia or myositis ossificans. Their radiographic appearance, however, is different.
Clinically, parosteal osteosarcoma presents as a palpable mass in patients who are usually a decade older than those with conventional osteosarcoma. Pain and inflammation, as well as limitations to articular motion, have been reported as early clinical symptoms [2].
Routine radiography, the initial imaging modality, typically shows an exophytic lobulated mass with dense cloud-like central sclerosis (Figure 1a). Initially, a small stalk-like focus of attachment and a cleavage plane between the mass and bone can be demonstrated (Figure 1b). The tumor tends to encase the bone with time and can invade into the medullary space; consequently, larger lesions may lack the finding of the cleavage plane. Debate exists regarding the effects of extension into the medullary space with respect to patient prognosis [3,4]. However, this extension is important to diagnose, as it will most certainly affect the surgical resection procedure. Both CT, which typically shows a well marginated, densely ossified mass attached to the cortex of the bone (Figure 2), and MR imaging, which typically shows a tumor of low signal intensity on all pulse sequences secondary to the internal fibrous and osteoid matrix, are sensitive and reliable in the detection of intramedullary tumor extension and in defining the cleavage plane [5].
Parosteal osteosarcoma will slowly enlarge and invade surrounding soft tissues, which can result in irregular, indistinct borders, and can be seen both on plain films as well as on cross sectional imaging (Figure 3a-g). Although myositis ossificans can attach to bone, the lesion tends to become smaller with time, has sharp borders, and is most dense in the periphery.
Due to the low metastatic incidence of parosteal osteosarcoma, we do not routinely obtain preoperative radionuclide bone scans. Furthermore, quantifying the abnormal radionuclide uptake by the lesion in question is not helpful in distinguishing a parosteal osteosarcoma from an indolent lesion such as the rare surface osteoma or myositis ossificans, both of which show a wide variation in radionuclide accumulation. Parosteal osteosarcoma has a tendency for local recurrence, and repeat plain film evaluation should be performed for any patient with abnormal postoperative symptoms at the surgical site.
It should be noted, however, that some studies have shown that there can be areas within a parosteal osteosarcoma which can have areas of high-grade anaplasia, similar to high-grade surface osteosarcoma, which would affect prognosis as well as imaging and surgical management [6]. These areas tend to be located peripherally in the tumor mass, measure one centimeter or greater in size, are poorly defined on CT, and have increased signal intensity on both T1 and T2 weighted pulse sequences. Additional findings in parosteal osteosarcomas with areas of high-grade anaplasia include large-sized lesions (greater than 10 cm), satellite lesions, or metastatic foci. Any tumor which is presumed to be a parosteal osteosarcoma and demonstrates an ill-defined soft tissue mass on CT or areas of increased signal intensity on MR should undergo biopsy for more accurate evaluation.
Periosteal osteosarcoma arises from the inner layer of the periosteum and is most commonly found in the diaphysis of the femur or tibia, particularly the anterior tibial cortex [7]. These lesions are moderately differentiated chondroblastic tumors.
Clinically, these lesions affect patients in the second and third decades of life who complain of pain, swelling, tenderness or palpated mass.
Plain film radiographs typically show an elongated incompletely mineralized lesion with cortical thickening, erosion and peripheral periosteal reaction (Figure 4a). Perpendicular bone spicules as well as circular densities representing a chondroid matrix can be seen within the tumor [3,7]. These lesions are not as dense as parosteal osteosarcoma. CT and MR imaging are reliable in detection of marrow invasion. CT will show the aggressive tumor with chondroid areas, spiculated periosteal bone, and possible soft tissue mass (Figure 4b). MR imaging is similar to imaging of cartilaginous tumors which show intermediate to low signal on T1 weighted sequences and areas of intermediate to high signal on T2 weighted sequences (Figure 5a-d) [8].
High-grade surface osteosarcoma has a similar clinical and radiographic appearance to periosteal osteosarcoma, although high-grade surface osteosarcoma tends to have a paucity of perpendicular bone spicules, can show more mineralization close to the bone surface, and can have foci of calcification [3].
Additionally, because of its aggressive nature, high-grade surface osteosarcoma, tends to be larger than other types of surface osteosarcoma when diagnosed, and may involve the entire circumference of the bone at initial presentation. The lesions are most commonly located in the diaphysis. The diagnosis is confirmed by pathology, as the histology shows a chondroblastic tumor similar to the more common periosteal osteosarcoma, although high-grade features are present. These high-grade components enhance the malignant potential of these tumors, which have a prognosis similar to intramedullary osteosarcoma. The radiographic evaluation would be similar to an intramedullary osteosarcoma.
Intracortical osteosarcoma arises in the cortex, usually in the femur or tibia, and has a predilection for the diaphysis. Clinically, patients who present with this tumor commonly complain of pain. Histologically, these tumors also are similar to conventional intramedullary osteosarcoma [9].
An ill-defined intracortical lytic process associated with cortical thickening is seen on routine radiographs. This lesion is almost always confined to the cortex; however, on rare occasions, intramedullary invasion or soft tissue mass is seen [10]. If additional imaging is needed for further characterization, CT is of value in identifying the internal matrix, cortical destruction, and surrounding bony reaction. If soft tissue or medullary extension is questionable, MR imaging should also be conducted.
Recently a new, rare, low-grade surface lesion termed osteochondroma-like parosteal osteosarcoma has been reported [11]. This tumor, which is found in a periosteal or juxtacortical location, is a low-grade malignancy without histologic anaplasia. The distinctive feature of this lesion is a superficial layer of spindle cells, which transform into a cartilaginous cap in which the malignant cells reside. Although this lesion has a similar appearance to a parosteal osteosarcoma, the malignant cells are located in the periphery of the lesion, rather than dispersed throughout the tumor, as is seen in the parosteal osteosarcoma. There is underlying benign lamellar bone. No reports of intramedullary extension by this tumor have been noted. The peak incidence for this tumor is in patients aged approximately thirty years, with a clinical presentation of a non-tender palpable mass.
Radiographs typically show a dense exophytic juxtacortical lesion adjacent to the surface of a long bone. In some examples, a radiolucent cleft is present. The underlying cortex may be obscured; no invasion should be present, however. No aggressive periosteal reaction or unossified soft tissue masses are present. CT scanning will confirm an intact cortex in cases where cortical preservation is questioned. MR imaging will show the central portion of the lesion to follow a fat signal, suggestive of mature bone as well as a thin cartilaginous cap, which should be less than 5 mm in thickness.
References
1. Meyer NR, Gagliardi JA, Lawson JP. Musculoskeletal radiology. In: Practical Guide to Diagnostic Imaging. St. Louis: CV Mosby, 1998: 261.
2. Greenfield GB. The solitary lesion. In: Greenfield GB ed. Radiology of Bone Disease. 4th ed. St. Louis: J.B. Lippincott, 1986: 558-582.
3. Schajowicz F, McGuire MH, Aranjo ES, Muscolo DL, Gitelis S. Osteosarcoma arising on the surfaces of long bones. J Bone Joint Surg (Am). 1988;70:555-564.
4. Okada K, Frassica FJ, Sim FH, Beabout JW, Bond JR, Unni KK. Parosteal osteosarcoma: a clinicopathological study. J Bone Joint Surg (Am). 1994;76:366-378.
5. Murphy MD, Robbin MR, McRae GA, Flemming DJ, Temple HT, Kransdorf MJ. The many faces of osteosarcoma. RadioGraphics. 1997;17:1205-1231.
6. Jelinek JS, Murphey MD, Kransdorf MJ, Shmookler BM, Malawer MM, Hur RC. Parosteal osteosarcoma: value of MR imaging and CT in the prediction of histologic grade. Radiology. 1996;201:837-842.
7. Resnick D, Kyriakos M, Greenway GD. Tumor-like diseases of bone: imaging and pathology of specific lesions. In: Resnick D ed. Diagnosis of Bone and Joint Disorders. 3rd ed. Philadelphia: Saunders, 1995: 3648-3697.
8. Wong KT, Haygood T, Dalinka MK, Kneeland B. Chondroblastic, grade 3 periosteal osteosarcoma. Skeletal Radiol. 1995;24:69-71.
9. Seeger LL, Yao L, Eckerdt JJ. Surface lesions of bone. Radiology. 1998;206:17-33.
10. Greenspan A, Wold L. Cortical osteosarcoma involving the medullary cavity and soft tissue: a case report. J Bone Joint Surg (Am). 1994;76:1399-1404.
11. Lin J, Yao L, Mirra JM, Bahk WJ. Osteochondroma like parosteal osteosarcoma: a report of six cases of a new entity. Am J Roentgenol. 1998;170:1571-1577.
Figure Legend
Figure 1a. Lateral radiograph of the knee in this patient with a proved parosteal osteosarcoma shows a densely lobulated ossified mass intimately associated with the posterior distal femur.
Figure 1b. Axial CT scan shows that this mass is fairly uniform in its ossific appearance with a stalk-like attachment to the posterior cortex of the femur. No underlying cortical or medullary invasion is present.
Figure 2. Axial CT scan of both femurs without contrast shows a lobulated calcified lesion with internal matrix ossification adherent to the posterior cortex which proved to be a parosteal osteosarcoma.
Figure 3a. This patient, with no trauma history, presented with a non-tender right thigh lump which showed a densely ossified mass adherent to the femur without underlying medullary invasion. A diagnosis of parosteal osteosarcoma was made. However, the patient refused any treatment.
Figure 3b. Frontal and oblique views obtained on the same patient returned to the department three years later, now with a much larger lobulated densely ossified mass which has progressed to encase the femur.
Figure 3c. Frontal and oblique views obtained on the same patient returned to the department three years later, now with a much larger lobulated densely ossified mass which has progressed to encase the femur.
Figure 3d. CT scan of the patient's right femur shows the residual stalk-like focus of attachment (arrow) as well as the tumor's growth around the femur. There appears to be a peripheral focus of the tumor which is undergoing mineralization (arrowheads).
Figure 3e. Axial proton density (TR 2000, TE 20) and T2 weighted (TR 2000, TE 80) pulse sequences show the persistent low signal intensity stalk-like mass expanding the overall diameter of the thigh. The more densely ossified components remain low in signal intensity while the poorly mineralized areas of the tumor are increased in signal intensity.
Figure 3f. Axial proton density (TR 2000, TE 20) and T2 weighted (TR 2000, TE 80) pulse sequences show the persistent low signal intensity stalk-like mass expanding the overall diameter of the thigh. The more densely ossified components remain low in signal intensity while the poorly mineralized areas of the tumor are increased in signal intensity.
Figure 3g. Axial T1 weighted (TR 800, TE 20) image at another level shows rounded areas of decreased signal intensity representing dense ossification while the poorly mineralized areas are isointense to muscle.
Figure 4a. Radiograph of the femur shows the aggressive cortical destruction with bone spicules and soft tissue mass in this lesion centered in the bone surface which proved to be a periosteal osteosarcoma.
Figure 4b. Axial CT scanning following IV contrast confirms the surface location of this tumor with cortical thickening and exuberant periosteal reaction. Marked edema with a peripheral rim of enhancement is seen (arrows).
Figure 5a. Lateral and coned down frontal view of the left lower leg in this patient with a periosteal osteosarcoma show periosteal elevation and thickening to the cortex in the tibia.
Figure 5b. Lateral and coned down frontal view of the left lower leg in this patient with a periosteal osteosarcoma show periosteal elevation and thickening to the cortex in the tibia.
Figure 5c. Sagittal T1 (TR 500, TE 30) and axial T2 (TR 2000, TE 80) better define the soft tissue component (arrows). Abnormal increased signal intensity is also present within the cortex while the medullary space appears uninvolved.
Figure 5d. Sagittal T1 (TR 500, TE 30) and axial T2 (TR 2000, TE 80) better define the soft tissue component (arrows). Abnormal increased signal intensity is also present within the cortex while the medullary space appears uninvolved.
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